Field of the Invention
The present invention relates to motorcycle tires, and in particular relates to a motorcycle tire that may improve straight-traveling stability as well as transient characteristic of cornering.
Description of the Related Art
Conventionally, a motorcycle tire including a tread portion provided with a groove has been proposed. Upon wet road traveling, the groove provided on the tread portion may disperse the water outward from under the tread portion to improve wet grip performance. On the other hand, the groove changes rigidity of the tread portion and therefore it may influence handling performance of the tire.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-506590 discloses a motorcycle tire having an improved groove arrangement that includes a zigzag central main groove disposed in a central region, a plurality of shoulder lateral grooves each extending from the central main groove and a plurality of shoulder sub grooves each extending along the shoulder lateral grooves to improve wet grip performance.
Unfortunately, the above mentioned motorcycle tire includes a tread portion formed as a curved manner with a small radius of curvature. Since the motorcycle tire has insufficient ground contact area during straight traveling, grip during straight traveling may not be enough. As a result, the motorcycle tire disclosed by the above mentioned Patent Publication has had a problem with respect to straight traveling stability.
Meanwhile, when the outer profile of the tread portion is formed as a large radius of curvature, the wet grip performance may be deteriorated. Furthermore, in the tire including a tread portion having a large radius of curvature, a gap between the normal of the tread outer surface and the normal on the ground becomes large when a large camber angle is given. Such a tire tends to exhibit the transient characteristic that suddenly changes when the camber angle becomes large. Accordingly, there was room for improvement on the straight traveling stability and transient characteristic while maintaining wet grip performance.